Simple blending of triglycerides into polymeric systems is known but the blends are limited as to their use as plasticizers or stabilizers. A more useful approach is to combine the triglycerides with the polymer as an interpenetrating polymer network as disclosed and claimed herein.
By definition, as interpenetrating network (IPN) is a material containing two or more polymers that have been vulcanized (crosslinked) in the presence of each other to form entangled networks with each other. It was discovered that the morphology of such intimate entanglement of two, or more, immiscible polymeric networks can lead to interesting physical properties that cannot be achieved by grafting, blending or other mixing techniques. Currently, products derived from IPN find applications ranging from false teeth to ion exchange resins, adhesives, high impact plastics, thermoplastics, vibration damping materials for outdoor, aircraft and machinery applications, high temperature alloys and medical devices.
Several IPNs are described in the literature containing plant oils and synthetic polymers. For example, alkyds and polyurethane IPNs (uralkyds) were prepared by casting films from hydrocarbon solutions followed Athawale, v.; Raut, s., Eur. Polym. J. 2002, 38, 2033-2040 and Raut, s.; Athawale, v., J. Polym. Sci., Part A: Polym. Chem. 1999, 37, (23), 4302-4308.) The resulting IPNs were useful as tough coatings and displayed high abrasion and chemical resistance.
Similarly, IPNs of alkyds and methacrylate polymers were described and the combination of the soft and the flexible poly(butyl methacrylate) with the hard and brittle alkyd produced a resin that had better physical properties than each individual component. (Athawale, V.; Raut, S., Poly. Int. 2001, 50, 1234-1240).
IPNs of castor oil triglycerides with poly(ethylene terephthalate) (PET) that were prepared by either ester-ester or ester-hydroxyl interchange reactions exhibited a high degree of toughness and faster crystallization rates than PET alone.
Barrett, L. W.; Sperling, L. H.; Gilmer, J. W.; Mylonakis, S. G., Semi-interpenetrating Polymer Networks Composed of Poly(ethylene terephthalate) and Castor Oil. In Interpenetrating Polymer Networks, American Chemical Society; 1994 Vol. 239, pp 489-516.)
IPNs prepared from castor oil based polyurethanes and styrene monomers were reported to be tough elastomers or reinforced plastics, depending on their composition while IPNs based on castor oil with acrylics were elastomers and exhibited good mechanical properties.
Many other IPNs have also been prepared from functionalized triglycerides of veronia, lesquerella, crambe, and linseed as well as their epoxidized derivatives with polystyrene and polyacrylics.
A recent comprehensive review of various IPNs of natural oils of synthetic polymers is also available at Sharma, V. Kundu, P. P., Prog. Polym. Sci., 2008, 33, (12), 1199-1215.
Most of the previous IPN work with triglycerides involved preparing homogeneous solutions of the triglycerides and the monomer and then polymerizing and crosslinking as phase separation occurs. Thus, the morphology of the resulting IPN was a function of the kinetics of the phase separation.
There are numerous IPNs containing polydimethylsiloxanes with a variety of synthetic polymers showing micro-phase separation and multi-phase structures due to the inherent immiscibility of polydimethysiloxanes with most organic polymers. Many of these IPNs have interesting and useful properties due to the high chain flexibility, low surface tension, high thermal stability and low Tg of the siloxane chain. Although there is a large number of silicone containing IPNs, no IPNs of silicone polymers and triglyceride oils are described or shown in the literature.
Instead of using organic solvents or relying on the solubility of the monomer in the triglycerides, it is also possible to prepare mixed oil in water emulsions of immiscible components and crosslink them before casting films. This method is known as Latex IPN. It consists of blending together two emulsions composed of components A and B, then crosslinking each independently with suitable crosslinkers.
Alternatively, latex A is crosslinked then another monomer B together with a crosslink agent and an initiator is added and polymerized. These latex IPNs combine both networks in a single latex particle and, as such, the IPN morphology is limited to the size of the latex particles while suspended in emulsion state. The effect of the addition sequence and polymer composition on inter- and the intra-particle micro-domains morphology (core/shell structures), as well as bicontinuous IPN structure inside the particle were reviewed.
In the instant invention, the focus is on Latex blended IPNs where two emulsions of incompatible polymers are prepared separately in one embodiment, and then combined together with a crosslink agent. Provided a common functional group is available on both polymers for crosslinking, the particles from both emulsions undergo intra-particle crosslinks while stills suspended in the water phase. Upon casting, additional inter-particle crosslinks take place between the coagulating particles to yield typical IPN morphology resins whereby the two phases are intimately mixed and crosslinked. Such IPN resins composed of plant oils and silicone could be useful as high release liners, law friction materials or as convenient one-package protective coatings.